As is well-known, air conditioners may serve to cool room air, for the purpose of which the air is drawn into the conditioner wherein it passes over a heat exchanger cooled by a refrigerant. Condensation thus forms on the surface of the heat exchanger and drips into a sump. In some arrangements, the condensate simply drains out of the sump, under the influence of gravity, through a pipe but in many cases it is essential or aesthetically desirable to lift the condensate, sometimes several meters, before discharging it to the desired location and it is common practice to use an electric pump for that purpose. Usually, the pump is of the reciprocating type and they are often noisy if air is drawn in. For this reason, it is important that the pump, when of such a type, operates only when the level of water in the sump is between pre-determined levels and so it is necessary to use a water level detection device.
The use of several alternative level detection devices has been proposed including mechanical devices such as magnetic float switches and devices which respond to changes in electrical conductivity. The former suffer from the disadvantage that they can readily become jammed by foreign matter such as metal or other particles or by the growth of biological matter on the moving parts. The latter often malfunction because the electrodes tend to become coated with electrically insulative material such as oil or fat or become permanently bridged by electrically conductive contaminants.
It is an object of the present invention to solve or mitigate the problems by proposing the use of an alternative form of level detection device.